Graded pressure drop type multi stage water injection device and method based on fracture observation

ABSTRACT

A graded pressure drop type multi stage water injection device and method based on fracture observation. The device includes a test probe, a propulsion system and a control system. The test probe includes a plugging device, a pressure conversion assembly and a connected pipe. The rubber bag is wrapped around the outer end of the water leakage pipe, is fixed to both ends of the joints through a fastening iron ring and forms a blocked cavity with the water leakage pipe. The device integrates the plugging and detection system, and uses the same external water source to operate the plugging process and detection process under their respective pressures, thereby making pressure conversion more stable, solving the problem of winding the drill pipe and the hose in the propulsion process, realizing multi stage measurement in each propulsion and improving measurement efficiency.

TECHNICAL FIELD

The present invention belongs to the technical field of permeability measurement of rock mass, and relates to a graded pressure drop type multi stage water injection device and method based on fracture observation.

BACKGROUND

The measurement of floor mining failure range in mine is an important parameter to indicate the occurrence state of coal and rock. It is a key basic parameter in the research of mine water prevention and control. Therefore, it is necessary to grasp the strata movement law and determine the height (or depth) of the mining failure zone in order to study the formation of water-inrush channel in mining surrounding rock. Series of detection equipment represented by “device for measuring leakage with double ends plugging of borehole” for in-site testing, have the problems of troublesome operation process and wire entanglement because the plugging operation table and the water supply operation table are independent and correspondingly connected with more than two pipelines and test probes in drill hole, and thus resulting in poor stability and low effectiveness during observation. In series of products, although the problem of single loop can be solved, there are problems of large conversion range of water pressure, poor conversion stability, difficult control of water pressure and easy mechanical failure. The prior art fails to simultaneously solve the above problems.

SUMMARY

The purpose of the present invention is to provide a graded pressure drop type multi stage water injection device and method based on fracture observation.

The technical solution of the present invention is:

A graded pressure drop type multi stage water injection device based on fracture observation, comprising a test probe, a propulsion system and a control system, wherein

the test probe comprises a plugging device, a pressure conversion assembly 49 and a connected pipe 28; the plugging device further consists of a plugging device at the front 35, a plugging device at the middle 36 and a plugging device at the rear end 37; a water injection cavity of No. 1 29 and a water injection cavity of No. 2 34 are formed among the plugging device at the front 35, the plugging device at the middle 36, the plugging device at the rear end 37 and drill holes 31; the pressure conversion assembly 49 is installed at the tail of the plugging device at the front 35 and the plugging device at the middle 36, including a first stage pressure converting device 6 and a second stage pressure converting device 39; a high pressure water source in the connected pipe 28 is graded and converted into a low pressure water source and then flows into the water injection cavity of No. 1 29 and the water injection cavity of No. 2 34 for detection; the plugging device comprises a water leakage pipe 3, a rubber bag 5 and a series of joints connected to both ends of the water leakage pipe 3; the rubber bag 5 is wrapped around the outer end of the water leakage pipe 3, is fixed to both ends of the joints through a fastening iron ring 24 and forms a blocked cavity 30 with the water leakage pipe 3.

The propulsion system comprises a drilling rig 14 and a drill pipe 12; the drill pipe 12 is a hollow pipe in which the high pressure water source can be delivered, and is in threaded connection with the test probe; the drilling rig 14 pushes the test probe to a designated region of the drill holes 31 through the drill pipe 12.

The control system comprises a control operation platform 38 which comprises a water release switch 15, a flow meter 16, a mechanical pressure gauge 17, an electronic pressure gauge 19 and a total control switch 18; the control operation platform 38 is connected with the drill pipe 12 through a high pressure resistant hose 13 and is responsible for providing the external water source with designated pressure to the test probe through the drill pipe 12.

The plugging device at the front 35 comprises a type I joint 2, a water leakage pipe 3, a type II joint 4 and a rubber bag 5; the type I joint 2, the type II joint 4 and the water leakage pipe 3 are in threaded connection; the rubber bag 5 is wrapped outside the water leakage pipe 3, is fixed outside the type I joint 2 and the type II joint 4 through a fastening iron ring 24, and forms a blocked cavity 30 with the water leakage pipe 3; the external end of the type I joint 2 is in threaded connection with a guide head 1; and the guide head 1 has a guide effect and is used to guide the test probe to smoothly slide in the drill hole 31.

The plugging device at the middle 36 comprises a type II joint 4, a water leakage pipe 3, a type III joint 7 and a rubber bag 5; the rubber bag 5 is fixed outside the type II joint 4 and the type III joint 7 through a fastening iron ring 24, and a water leakage hole 25 is formed in the water leakage pipe 3.

The plugging device at the rear end 37 comprises two type III joints 7, a water leakage pipe 3 and a rubber bag 5; and the rubber bag 5 is fixed between the two type III joints 7 through a fastening iron ring 24. The external part of the type III joints 7 is in threaded connection with a circular baffle 11; the diameter of the circular baffle 11 is larger than that of the rubber bag 5 to prevent the rubber bag 5 from falling; and the circular baffle 11 and the type III joints 7 are in threaded connection and are detachable to facilitate the replacement of the rubber bag 5.

The external water source enters the blocked cavity 30 through the water leakage hole 25 in the plugging device at the front 35, the plugging device at the middle 36 and the plugging device at the rear end 37; the corresponding rubber bag 5 is inflated to respectively form the water injection cavity of No. 1 29 and the water injection cavity of No. 2 34 with the drill holes 31.

The left end and the right end of the pressure conversion assembly 49 are respectively in threaded connection with the connected pipe 28 and a type II joint 4; the high pressure water source in the connected pipe 28 is graded and converted by the first stage pressure converting device 6 and the second stage pressure converting device 39 successively into a low pressure water source and delivered into the water injection cavity.

A central through hole 32 and four peripheral through holes 33 are formed in the first stage pressure converting device 6; the four peripheral through holes 33 are symmetrically distributed around the central through hole 32.

The central through hole 32 is a ladder hole, where the left aperture is less than the right aperture; side drain holes 20 are formed in the side walls of the peripheral through holes 33.

A conversion body 10, an inner spring 9 and a regulating screw 8 are successively installed in the peripheral through holes 33; threads are arranged on the left inner walls of the peripheral through holes 33 and are matched with the regulating screw 8 so that the regulating screw 8 rotates and compresses the inner spring within a certain range of the peripheral through holes 33 to control the opening pressure of the conversion body 10.

A hexagonal through hole 21 is formed in the side wall of the regulating screw 8 so that rotation of the regulating screw 8 is facilitated and feedback water pressure acts on the left end surface of the conversion body 10.

The conversion body 10 is a cylinder of unequal diameters, and the diameter of the left end surface of the conversion body 10 is larger than that of the right end surface; a sealed conical surface 26 is at the transition of the cylinder of unequal diameters, and coincides with the sealed conical surface 26 of the inner wall of the peripheral through holes 33; the sealed conical surface 26 has an angle of 30°.

An “L”-shaped limber of No. 1 23 is formed in the conversion body 10; an annular flume 22 is formed in a cylindrical external surface near the left end surface of the conversion body 10; the limber of No. 1 23 is communicated with the annular flume 22; and when the conversion body 10 moves to the left driven by the outside water source, the annular flume 22 is communicated with the side drain holes 20.

The second stage pressure converting device 39 comprises an external annular component 40, an internal annular component 41, an annular conversion body 42, an external spring 47 and a cross filiform ring 48; a thread is arranged on the right inner wall of the external annular component 40, is sheathed on the right outer wall of the first stage pressure converting device 6 and forms a central transitional cavity 50 with the first stage pressure converting device 6; and the side drain holes 20 and the hexagonal through hole 21 are communicated with the central transitional cavity 50.

The internal annular component 40 is in the shape of a cylindrical ring, and a thread is arranged on the inner wall of the internal annular component 40 and is wrapped around the outer wall of the connected pipe 28; four protruding parts 46 are arranged on the outer wall to limit the maximum leftward movement range of the annular conversion body 42; water collecting slots 44 and water diversion holes 45 are disposed in the pipe wall of the internal annular component 41; four water diversion holes 45 are disposed and are respectively vertically communicated with the water collecting slots 44 to diverse and drain water in the water collecting slots 44.

The annular conversion body 42 is positioned between the external annular component 40 and the internal annular component 41 and can slide left and right along the surface of the internal annular component 41.

Four “L”-shaped limbers of No. 2 43 are correspondingly formed in the annular conversion body 42; when the annular conversion body 42 moves to the left, the limbers of No. 2 43 are communicated with the water collecting slots 44 to deliver the high pressure water source in the central transitional cavity 60 into the water collecting slots 44; at this moment, the left end surface of the annular conversion body 42 just comes into contact with the protruding part 46; and the diameter of the left end surface of the annular conversion body 42 is larger than that of the right end surface, and the sealed conical surface 26 matched with the external annular component 40 is arranged in the middle connected position.

The external spring 47 is positioned between the annular conversion body 42 and the cross filiform ring 48, and has the same diameter as the left end surface of the annular conversion body 42.

The cross filiform ring 48 is in the shape of “cross”, and the middle position thereof is circular; a thread is arranged on the inner wall of the cross filiform ring 48 and is matched with the internal annular component 41; the cross filiform ring 48 rotates on the thread by means of an external tool to change the compression extent of the external spring 47 so as to control the opening pressure of the annular conversion body 42.

The working principle of the first stage pressure converting device 6 is:

(1) when the conversion body 10 satisfies P_(mid)S_(left)+k_(inner)x≤P_(right)S_(right), the conversion body 10 moves to the left, and then the annular flume 22 is communicated with the side drain holes 20 to supply water into the central transitional cavity 50 to realize first stage pressure drop;

(2) when the conversion body 10 satisfies P_(mid)S_(left)+k_(inner)x≥P_(right)S_(right), the conversion body 10 moves to the right, and then the annular flume 22 is closed by the inner walls of the peripheral through holes 33 to stop supplying water into the central transitional cavity 50;

(3) if P_(right) is too large, in order to prevent extreme water pressure of P_(right) from damaging the inner wall of the drill hole 31 in the water injection cavity through the pressure conversion assembly 49, the conversion body 10 moves to the left under the action of the outside water source until the annular flume 22 moves to the left end of the side drain hole 20 and forms another closing role on the inner walls of the peripheral through holes 33.

P_(mid) is the water source pressure of the central transitional cavity 50, which is generally about 0.8 to 1 MPa. P_(right) is the pressure of the supplied water source in the connected pipe 28, which is generally about 1.5 MPa; S_(left) is the area of the left end surface of the conversion body 10; S_(right) is the area of the right end surface of the conversion body 10; k_(inner) is an elastic coefficient of the inner spring 9; and x is compression length.

The working principle of the second stage pressure converting device 39 is:

(1) when the annular conversion body 42 satisfies P_(left)S_(left)+k_(outer)x≤P_(mid)S_(right), the annular conversion body 42 moves to the left, and then the limbers of No. 2 43 are communicated with the water collecting slots 44 to inject low pressure water into the water injection cavity through the water diversion holes 45 to realize second stage pressure drop;

(2) when the annular conversion body 42 satisfies P_(left)S_(left)+k_(outer)x≥P_(mid)S_(right), the annular conversion body 42 moves to the right, and then the limbers of No. 2 43 are closed by the outer wall of the internal annular component 41 to stop supplying water into the water injection cavity.

Wherein P_(left) is the observed water source pressure of the water injection cavity, which is generally about 0.2 to 0.5 MPa; P_(mid) is the pressure of the water source in the central transitional cavity 50, which is generally about 0.8 to 1 MPa; S_(left) is the contact area between water and the left end surface of the annular conversion body 42; S_(right) is the contact area between water and the right end surface of the annular conversion body 42; and k_(outer) is an elastic coefficient of the external spring 47; and x is compression length.

The control operation platform 38 comprises a water release switch 15, a flow meter 16, a mechanical pressure gauge 17, a total control switch 18 and an electronic pressure gauge 19; the water release switch 15 is responsible for releasing pressure water in the test probe after pressurized pressure testing completed so that the rubber bag 5 is out of contact with the drill hole 31 to facilitate the drilling rig 14 in pushing the test probe; the total control switch 18 is responsible for interruption of the external water source supply; the flow meter 16 is responsible for displaying real-time water input from the external water source to the test probe; the mechanical pressure gauge 17 is compared with the reading of the electronic pressure gauge 19 for inspection; and if the mechanical pressure gauge 17 is roughly equal to the reading, then the pressure is effective.

A graded pressure drop type multi stage water injection method based on fracture observation, comprises the following steps:

(1) constructing drill holes (31): constructing three to five drill holes with different directions and inclined angles in the region of rock mass (27) to be detected through the drilling rig (14) in accordance with predesigned construction requirements; the drill holes (31) having a diameter of 89 mm and a length of about 70 m; and cleaning scraps in the drill holes (31);

(2) installing equipment: installing all components of the test probe; successively connecting the drilling rig (14), the drill pipe (12), the high pressure resistant hose (13) and the control operation platform (38); and then pushing the test probe to the initial positions of the drill holes (31) through the drilling rig (14);

(3) seal inspection: firstly, turning off a water release switch (15) of the control operation platform (38); turning on the total control switch (18) to provide detection water pressure for the test probe; conducting a plugging seal inspection on the rubber bag (5); conducting next operation if there is no obvious water leakage phenomenon; otherwise, returning to operation of step (2) to inspect the connection and installation among all components until qualified;

(4) detecting water leakage rate: conducting pressurized-water test after passing the seal inspection; starting the test probe to be in the initial position; turning off the water release switch (15) on the control operation platform (38) and turning on the total control switch (18) to provide a high pressure water source for the test probe; allowing the water source to enter the blocked cavity 30 through the connected pipe (28) and the water leakage pipe (3); inflating the rubber bags (5) of the plugging device at the front (35), the plugging device at the middle (36) and the plugging device at the rear end (37) to form a water injection cavity of No. 1 (29) and a water injection cavity of No. 2 (34) with the drill holes (31); adjusting the pressure of the external water source to gradually rise to 1.5 MPa for only allowing the pressure conversion assembly (49) of the water injection cavity of No. 1 (29) to inject low pressure water into the water injection cavity of No. 1 (29), and recording the steady reading Q_(i1) of the flow meter after the reading of the flow meter is steady; continuously increasing the pressure of the external water source to 1.7 MPa for stopping supplying water into the water injection cavity of No. 1 (29) at this moment because the first stage pressure converting device (6) of the water injection cavity of No. 1 (29) is turned off due to the increase of the pressure, and starting the pressure conversion assembly (49) of the water injection cavity of No. 2 (34) to inject water into the water injection cavity of No. 2 (34); and recording the steady reading Q_(i2) of the flow meter after the reading of the flow meter is steady, and recording detection distances L_(i1) and L_(i2);

(5) pressure relief propulsion: turning off the total control switch (18); turning on the water release switch (15) to release the pressure of the blocked cavity (30); turning off the water release switch (15) after the rubber bag (5) is out of contact with the drill holes (31); taking another drill pipe (12) to connect to the test probe; pushing the test probe to a next detection region through the drilling rig (14); and repeating the operation of step (4) until all lengths of the drill holes is detected;

(6) calculation and analysis: respectively drawing flow distribution maps in different drill holes according to the length of the drill holes (31) and corresponding injected water leakage of drilling hole; analyzing fracture development and permeability characteristics at different positions within the length range of the drill holes; and further calculating failure range of the rock mass within different spatial ranges by combining with the inclined angles of the drill holes in different directions with accumulated successive water leakage length L_(n1)+L_(n2) (n=1+2+ . . . +k).

The present invention has the following beneficial effects that:

(1) The present invention proposes a graded pressure drop type multi stage water injection device based on fracture observation. Compared with the prior art, the device realizes plugging and leak detection integration of the test probe, reduces the number of the pipelines that work simultaneously in the drill holes as 1 pipeline, solves the multi pipe entanglement problem in the drill holes during propulsion and enhances the stability of the measurement process for the failure range of rock mass.

(2) The device solves the problem that the plugging process and the observation process operate under respective pressures through the same outside water source, avoids damaging the borehole cracks caused by ultrahigh pressure of the observation water source and enhances the accuracy of the measurement process of the failure range of rock mass.

(3) The device conducts gradient pressure conversion through the first stage pressure converting device and the second stage pressure converting device, enhances the stability of the working process of the pressure conversion assembly through the design of the sealed conical surface, adjusts compression length of the spring through screws (cross filiform rings), and controls the conversion body (annular conversion body) to have different opening pressures and conversion pressures so that the pressure adjusting range is more extensive and can adapt to different work needs.

(4) The design of the annular flume and the water collecting slots solves the problem that the limbers do not correspond to the water outlets, and ensures that the water in the limbers can flow through the annular flume to the converting device outlet no matter how the conversion body (annular conversion body) rotates.

(5) The device realizes multi stage successive measurement process at one propulsion and improves the observation efficiency of each propulsion. Compared with the traditional device, the device enhances the detection speed and shortens the detection time.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an overall structure and observation state of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 2 is a schematic diagram of a pressure relief propulsion state of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 3 is a structural schematic diagram of a test probe of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 4 is a structural schematic diagram of a plugging device at the front of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 5 is a structural schematic diagram of a plugging device at the middle of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 6 is a structural schematic diagram of a plugging device at the rear end of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 7 is a structural schematic diagram of a pressure conversion assembly of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 8(a) is a main view of a first stage pressure converting device of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 8(b) is a side view of a first stage pressure converting device of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 9(a) is a static state diagram of a first stage pressure converting device of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 9(b) is an operating state diagram of a first stage pressure converting device of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 10(a) is a main view of a conversion body structure of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 10(b) is a rear view of a conversion body structure of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 10(c) is a side view of a conversion body structure of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 11(a) is a main view of a regulating screw structure of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 11(b) is a side view of a regulating screw structure of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 12 is a structural schematic diagram of a second stage pressure converting device of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 13 is a structural schematic diagram of an annular conversion body of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 14(a) is a main view of an internal annular component structure of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention;

FIG. 14(b) is a side view of an internal annular component structure of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention; and

FIG. 15 is a structural schematic diagram of a cross filiform ring of a graded pressure drop type multi stage water injection device based on fracture observation in the present invention.

In the figures: 1 guide head; 2 type I joint; 3 water leakage pipe; 4 type II joint; 5 rubber bag; 6 first stage pressure converting device; 7 type III joint; 8 regulating screw; 9 inner spring; 10 conversion body; 11 circular baffle; 12 drill hole; 13 high pressure resistant hose; 14 drilling rig; 15 water release switch; 16 flow meter; 17 mechanical pressure gauge; 18 total control switch; 19 electronic pressure gauge; 20 side drain hole; 21 hexagonal through hole; 22 annular flume; 23 limber of No. 1; 24 fastening iron ring; 25 water leakage hole; 26 sealed conical surface; 27 rock mass to be detected; 28 connected pipe; 29 water injection cavity of No.1; 30 blocked cavity; 31 drill hole; 32 central through hole; 33 peripheral through hole; 34 water injection cavity of No. 2; 35 plugging device at the front; 36 plugging device at the middle; 37 plugging device at the rear end; 38 control operation platform; 39 second stage pressure converting device; 40 external annular component; 41 internal annular component; 42 annular conversion body; 43 limber of No. 2; 44 water collecting slot; 45 water diversion hole; 46 protruding part; 47 external spring; 48 cross filiform ring; 49 pressure conversion assembly; and 50 central transitional cavity.

DETAILED DESCRIPTION

The present invention will be further described in detail below in combination with specific embodiments.

As shown in FIGS. 1-3, a graded pressure drop type multi stage water injection device based on fracture observation comprises a test probe, a propulsion system and a control system, wherein

the test probe comprises a plugging device, a pressure conversion assembly 49 and a connected pipe 28; the plugging device further consists of a plugging device at the front 35, a plugging device at the middle 36 and a plugging device at the rear end 37; a water injection cavity of No. 1 29 and a water injection cavity of No. 2 34 are formed among the plugging device at the front 35, the plugging device at the middle 36, the plugging device at the rear end 37 and drill holes; the pressure conversion assembly 49 is installed at the tail of the plugging device at the front 35 and the plugging device at the middle 36, including a first stage pressure converting device 6 and a second stage pressure converting device 39; a high pressure water source in the connected pipe 28 is graded and converted into a low pressure water source and then flows into the water injection cavity of No. 1 29 and the water injection cavity of No. 2 34 for detection; the plugging device comprises a water leakage pipe 3, a rubber bag 5 and a series of joints connected to both ends of the water leakage pipe 3; the rubber bag 5 is wrapped around the outer end of the water leakage pipe 3, is fixed to both ends of the joints through a fastening iron ring 24 and forms a blocked cavity 30 with the water leakage pipe 3;

The propulsion system comprises a drilling rig 14 and a drill pipe 12; the drill pipe 12 is a hollow pipe in which the high pressure water source can be delivered, and is in threaded connection with the test probe; the drilling rig 14 pushes the test probe to a designated region of the drill holes 31 through the drill pipe 12.

The control system comprises a control operation platform 38 which comprises a water release switch 15, a flow meter 16, a mechanical pressure gauge 17, an electronic pressure gauge 19 and a total control switch 18; the control operation platform 38 is connected with the drill pipe 12 through a high pressure resistant hose 13 and is responsible for providing the external water source with designated pressure to the test probe through the drill pipe 12.

The plugging device at the front comprises a type I joint 2, a water leakage pipe 3, a type II joint 4 and a rubber bag 5; the type I joint 2, the type II joint 4 and the water leakage pipe 3 are in threaded connection; the rubber bag 5 is wrapped outside the water leakage pipe 3, is fixed outside the type I joint 2 and the type II joint 4 through a fastening iron ring 24, and forms a blocked cavity 30 with the water leakage pipe 3; the external end of the type I joint 2 is in threaded connection with a guide head 1; and the guide head 1 has a guide effect and is used to guide the test probe to smoothly slide in the drill hole 31.

The plugging device at the middle 36 comprises a type II joint 4, a water leakage pipe 3, a type III joint 7 and a rubber bag 5; the rubber bag 5 is fixed outside the type II joint 4 and the type III joint 7 through a fastening iron ring 24, and a water leakage hole 25 is formed in the water leakage pipe 3.

The plugging device at the rear end 37 comprises two type III joints 7, a water leakage pipe 3 and a rubber bag 5; and the rubber bag 5 is fixed between the two type III joints 7 through a fastening iron ring 24. The external part of the type III joints 7 is in threaded connection with a circular baffle 11; the diameter of the circular baffle 11 is larger than that of the rubber bag 5 to prevent the rubber bag 5 from falling; and the circular baffle 11 and the type III joints 7 are in threaded connection and are detachable to facilitate the replacement of the rubber bag 5.

The external water source enters the blocked cavity 30 through the water leakage hole 25 in the plugging device at the front 35, the plugging device at the middle 36 and the plugging device at the rear end 37; the corresponding rubber bag 5 is inflated to respectively form the water injection cavity of No. 1 29 and the water injection cavity of No. 2 34 with the drill holes 31.

The left end and the right end of the pressure conversion assembly 49 are respectively in threaded connection with the connected pipe 28 and a type II joint 4; the high pressure water source in the connected pipe 28 is graded and converted by the first stage pressure converting device 6 and the second stage pressure converting device 39 successively into a low pressure water source and delivered into the water injection cavity.

A central through hole 32 and four peripheral through holes 33 are formed in the first stage pressure converting device 6; the four peripheral through holes 33 are symmetrically distributed around the central through hole 32.

The central through hole 32 is a ladder hole, where the left aperture is less than the right aperture; ide drain holes 20 are formed in the side walls of the peripheral through holes (33).

A conversion body (10), an inner spring (9) and a regulating screw (8) are successively installed in the peripheral through holes (33); threads are arranged on the left inner walls of the peripheral through holes 33 and are matched with the regulating screw 8 so that the regulating screw 8 rotates and compresses the inner spring within a certain range of the peripheral through holes 33 to control the opening pressure of the conversion body 10.

A hexagonal through hole 21 is formed in the side wall of the regulating screw 8 so that rotation of the regulating screw 8 is facilitated and feedback water pressure acts on the left end surface of the conversion body 10.

The conversion body 10 is a cylinder of unequal diameters, and the diameter of the left end surface of the conversion body 10 is larger than that of the right end surface; a sealed conical surface 26 is at the transition of the cylinder of unequal diameters, and coincides with the sealed conical surface 26 of the inner wall of the peripheral through holes 33; the sealed conical surface 26 has an angle of 30°.

An “L”-shaped limber of No. 1 23 is formed in the conversion body 10; an annular flume 22 is formed in a cylindrical external surface near the left end surface of the conversion body 10; the limber of No. 1 23 is communicated with the annular flume 22; and when the conversion body 10 moves to the left driven by the outside water source, the annular flume 22 is communicated with the side drain holes 20.

The second stage pressure converting device 39 comprises an external annular component 40, an internal annular component 41, an annular conversion body 42, an external spring 47 and a cross filiform ring 48; a thread is arranged on the right inner wall of the external annular component 40, is sheathed on the right outer wall of the first stage pressure converting device 6 and forms a central transitional cavity 50 with the first stage pressure converting device 6; the side drain holes 20 and the hexagonal through hole 21 are communicated with the central transitional cavity 50.

The internal annular component 40 is in the shape of a cylindrical ring, and a thread is arranged on the inner wall of the internal annular component 40 and is wrapped around the outer wall of the connected pipe 28; four protruding parts 46 are arranged on the outer wall to limit the maximum leftward movement range of the annular conversion body 42; water collecting slots 44 and water diversion holes 45 are disposed in the pipe wall of the internal annular component 41; four water diversion holes 45 are disposed and are respectively vertically communicated with the water collecting slots 44 to diverse and drain water in the water collecting slots 44.

The annular conversion body 42 is positioned between the external annular component 40 and the internal annular component 41 and can slide left and right along the surface of the internal annular component 41.

Four “L”-shaped limbers of No. 2 43 are correspondingly formed in the annular conversion body 42; when the annular conversion body moves to the left, the limbers of No. 2 43 are communicated with the water collecting slots 44 to deliver the high pressure water source in the central transitional cavity 60 into the water collecting slots 44; at this moment, the left end surface of the annular conversion body 42 just comes into contact with the protruding part 46; the diameter of the left end surface of the annular conversion body 42 is larger than that of the right end surface, and the sealed conical surface 26 matched with the external annular component 40 is arranged in the middle connected position.

The external spring 47 is positioned between the annular conversion body 42 and the cross filiform ring 48, and has the same diameter as the left end surface of the annular conversion body 42.

The cross filiform ring 48 is in the shape of “cross”, and the middle position thereof is circular; a thread is arranged on the inner wall of the cross filiform ring 48 and is matched with the internal annular component 41; the cross filiform ring 48 rotates on the thread by means of an external tool to change the compression extent of the external spring 47 so as to control the opening pressure of the annular conversion body 42.

The working principle of the first stage pressure converting device 6 is:

(1) when the conversion body 10 satisfies P_(mid)S_(left)+k_(inner)x≤P_(right)S_(right), the conversion body 10 moves to the left, and then the annular flume 22 is communicated with the side drain holes 20 to supply water into the central transitional cavity 50 to realize first stage pressure drop;

(2) when the conversion body 10 satisfies P_(mid)S_(left)+k_(inner)x≥P_(right)S_(right), the conversion body 10 moves to the right, and then the annular flume 22 is closed by the inner walls of the peripheral through holes 33 to stop supplying water into the central transitional cavity 50;

(3) if P_(right) is too large, in order to prevent extreme water pressure of P_(right) from damaging the inner wall of the drill hole 31 in the water injection cavity through the pressure conversion assembly 49, the conversion body 10 moves to the left under the action of the outside water source until the annular flume 22 moves to the left end of the side drain hole 20 and forms another closing role on the inner walls of the peripheral through holes 33.

Wherein P_(mid) is the water source pressure of the central transitional cavity 50, which is generally about 0.8 to 1 MPa. P_(right) is the pressure of the supplied water source in the connected pipe 28, which is generally about 1.5 MPa; S_(left) is the area of the left end surface of the conversion body 10; S_(right) is the area of the right end surface of the conversion body 10; k_(inner) is an elastic coefficient of the inner spring 9; and x is compression length.

The working principle of the second stage pressure converting device 39 is:

(1) when the annular conversion body 42 satisfies P_(left)S_(left)+k_(outer)x≤P_(mid)S_(right), the annular conversion body 42 moves to the left, and then the limbers of No. 2 43 are communicated with the water collecting slots 44 to inject low pressure water into the water injection cavity through the water diversion holes 45 to realize second stage pressure drop;

(2) when the annular conversion body 42 satisfies P_(left)S_(left)+k_(outer)x≥P_(mid)S_(right), the annular conversion body 42 moves to the right, and then the limbers of No. 2 43 are closed by the outer wall of the internal annular component 41 to stop supplying water into the water injection cavity.

Wherein P_(left) is the observed water source pressure of the water injection cavity, which is generally about 0.2 to 0.5 MPa; P_(mid) is the pressure of the water source in the central transitional cavity 50, which is generally about 0.8 to 1 MPa; S_(left) is the contact area between water and the left end surface of the annular conversion body 42; S_(right) is the contact area between water and the right end surface of the annular conversion body 42; and k_(outer) is an elastic coefficient of the external spring 47; and x is compression length.

The control operation platform 38 comprises a water release switch 15, a flow meter 16, a mechanical pressure gauge 17, a total control switch 18 and an electronic pressure gauge 19; the water release switch 15 is responsible for releasing pressure water in the test probe after pressurized pressure testing completed so that the rubber bag 5 is out of contact with the drill hole 31 to facilitate the drilling rig 14 in pushing the test probe; the total control switch 18 is responsible for interruption of the external water source supply; the flow meter 16 is responsible for displaying real-time water input from the external water source to the test probe; the mechanical pressure gauge 17 is compared with the reading of the electronic pressure gauge 19 for inspection; and if the mechanical pressure gauge 17 is roughly equal to the reading, then the pressure is effective.

A graded pressure drop type multi stage water injection method based on fracture observation comprises the following steps:

(1) constructing drill holes 31: constructing three to five drill holes with different directions and inclined angles a in the region of rock mass 27 to be detected through the drilling rig 14 in accordance with predesigned construction requirements; the drill holes 31 having a diameter of 89 mm and a length of about 70 m; and cleaning scraps in the drill holes 31;

(2) installing equipment: installing all components of the test probe; successively connecting the drilling rig 14, the drill pipe 12, the high pressure resistant hose 13 and the control operation platform 38; and then pushing the test probe to the initial positions of the drill holes 31 through the drilling rig 14;

(3) seal inspection: firstly, turning off a water release switch 15 of the control operation platform 38; turning on the total control switch 18 to provide detection water pressure for the test probe; conducting a plugging seal inspection on the rubber bag 5; conducting next operation if there is no obvious water leakage phenomenon; otherwise, returning to operation of step (2) to inspect the connection and installation among all components until qualified;

(4) detecting water leakage rate: conducting pressurized-water test after passing the seal inspection; starting the test probe to be in the initial position; turning off the water release switch 15 on the control operation platform 38 and turning on the total control switch 18 to provide a high pressure water source for the test probe; allowing the water source to enter the blocked cavity 30 through the connected pipe 28 and the water leakage pipe 3; inflating the rubber bags 5 of the plugging device at the front 35, the plugging device at the middle 36 and the plugging device at the rear end 37 to form a water injection cavity of No. 1 29 and a water injection cavity of No. 2 34 with the drill holes 31; adjusting the pressure of the external water source to gradually rise to 1.5 MPa for only allowing the pressure conversion assembly 49 of the water injection cavity of No. 1 29 at this moment to inject low pressure water into the water injection cavity of No. 1 29, and recording the steady reading Q_(i1) of the flow meter after the reading of the flow meter is steady; continuously increasing the pressure of the external water source to 1.7 MPa for stopping supplying water into the water injection cavity of No. 1 29 at this moment because the first stage pressure converting device 6 of the water injection cavity of No. 1 29 is turned off due to the increase of the pressure, and starting the pressure conversion assembly 49 of the water injection cavity of No. 2 34; and recording the steady reading Q_(i2) of the flow meter after the reading of the flow meter is steady, and recording detection distances L_(i1) and L_(i2);

(5) pressure relief propulsion: turning off the total control switch 18; turning on the water release switch 15 to release the pressure of the blocked cavity 30; turning off the water release switch 15 after the rubber bag 5 is out of contact with the drill holes 31; taking another drill pipe 12 to connect to the test probe; pushing the test probe to a next detection region through the drilling rig 14; and repeating the operation of step (4) until all lengths of the drill holes is detected;

(6) calculation and analysis: respectively drawing flow distribution maps in different drill holes 31 according to the length of the drill holes 31 and corresponding injected water leakage of drilling hole; analyzing fracture development and permeability characteristics at different positions within the length range of the drill holes; and further calculating failure range of the rock mass within different spatial ranges by combining with the inclined angles of the drill holes in different directions with accumulated successive water leakage length L_(n1)+L_(n2)(n=1+2+ . . . +k).

The part not described in the present invention can be realized by adopting or referring to the prior art.

Although many terms such as the conversion body 10, the pressure conversion assembly 49 and the first stage pressure converting device 6 are used herein, it is also possible to use other terms. Simple replacements made to these terms by those skilled in the art under the enlightenment of the present invention shall be included within the protection scope of the present invention. 

1. A graded pressure drop type multi stage water injection device based on fracture observation, comprising a test probe, a propulsion system and a control system, wherein the test probe comprises a plugging device, a pressure conversion assembly and a connected pipe); the plugging device further consists of a plugging device at the front, a plugging device at the middle and a plugging device at the rear end; a water injection cavity of No. 1 and a water injection cavity of No. 2 are formed among the plugging device at the front, the plugging device at the middle, the plugging device at the rear end and drill holes; the pressure conversion assembly is installed at the tail of the plugging device at the front; and the plugging device at the middle, including a first stage pressure converting device and a second stage pressure converting device; a high pressure water source in the connected pipe is graded and converted into a low pressure water source and then flows into the water injection cavity of No. 1 and the water injection cavity of No. 2 for detection; the plugging device comprises a water leakage pipe, a rubber bag and a series of joints connected to both ends of the water leakage pipe; the rubber bag is wrapped around the outer end of the water leakage pipe, is fixed to both ends of the joints through a fastening iron ring and forms a blocked cavity with the water leakage pipe; the propulsion system comprises a drilling rig and a drill pipe the drill pipe is a hollow pipe in which the high pressure water source can be delivered, and is in threaded connection with the test probe; the drilling rig pushes the test probe to a designated region of the drill holes through the drill pipe; the control system comprises a control operation platform which comprises a water release switch, a flow meter, a mechanical pressure gauge, an electronic pressure gauge and a total control switch; the control operation platform is connected with the drill pipe through a high pressure resistant hose, and is responsible for providing the external water source with designated pressure to the test probe through the drill pipe; the external water source enters the blocked cavity through the water leakage hole in the plugging device at the front, the plugging device at the middle and the plugging device at the rear end; the corresponding rubber bag is inflated to respectively form the water injection cavity of No. 1 and the water injection cavity of No. 2 with the drill hole; the left end and the right end of the pressure conversion assembly are respectively in threaded connection with the connected pipe and a type II joint; the high pressure water source in the connected pipe is graded and converted by the first stage pressure converting device and the second stage pressure converting device successively into a low pressure water source and delivered into the water injection cavity; a central through hole and four peripheral through holes are formed in the first stage pressure converting device; the four peripheral through holes are symmetrically distributed around the central through hole; the central through hole is a ladder hole, where the left aperture is less than the right aperture; side drain holes are formed in the side walls of the peripheral through holes; a conversion body, an inner spring and a regulating screw are successively installed in the peripheral through holes; threads are arranged on the left inner walls of the peripheral through holes and are matched with the regulating screw so that the regulating screw rotates and compresses the inner spring within a certain range of the peripheral through holes to control the opening pressure of the conversion body; a hexagonal through hole is formed in the side wall of the regulating screw so that rotation of the regulating screw is facilitated and feedback water pressure acts on the left end surface of the conversion body; the conversion body is a cylinder of unequal diameters, and the diameter of the left end surface of the conversion body is larger than that of the right end surface; a sealed conical surface is at the transition of the cylinder of unequal diameters, and coincides with the sealed conical surface of the inner wall of the peripheral through hole; the sealed conical surface has an angle of 30°; an “L”-shaped limber of No. 1 is formed in the conversion body; an annular flume is formed in a cylindrical external surface near the left end surface of the conversion body; the limber of No. 1 is communicated with the annular flumes; when the conversion body moves to the left driven by the outside water source, the annular flume is communicated with the side drain holes; the second stage pressure converting device comprises an external annular component, an internal annular component, an annular conversion body, an external spring and a cross filiform ring; a thread is arranged on the right inner wall of the external annular component, is sheathed on the right outer wall of the first stage pressure converting device, and forms a central transitional cavity with the first stage pressure converting device; the side drain holes and the hexagonal through hole are communicated with the central transitional cavity; the internal annular component is in the shape of a cylindrical ring, and a thread is arranged on the inner wall of the internal annular component and is wrapped around the outer wall of the connected pipe; four protruding parts are arranged on the outer wall to limit the maximum leftward movement range of the annular conversion body; water collecting slots and water diversion holes are disposed in the pipe wall of the internal annular component; four water diversion holes are disposed and are respectively vertically communicated with the water collecting slots to diverse and drain water in the water collecting slots; the annular conversion body is positioned between the external annular component and the internal annular component and can slide left and right along the surface of the internal annular component; four “L”-shaped limbers of No. 2 are correspondingly formed in the annular conversion body; when the annular conversion body moves to the left, the limbers of No. 2 are communicated with the water collecting slots to deliver the high pressure water source in the central transitional cavity into the water collecting slots; at this moment, the left end surface of the annular conversion body just comes into contact with the protruding part; the diameter of the left end surface of the annular conversion body is larger than that of the right end surface, and the sealed conical surface matched with the external annular component is arranged at the intermediate connection position; the external spring is positioned between the annular conversion body and the cross filiform ring, and has the same diameter as the left end surface of the annular conversion body; the cross filiform ring is in the shape of “cross”, and the middle position thereof is circular; a thread is arranged on the inner wall of the cross filiform ring and is matched with the internal annular component; the cross filiform ring rotates on the thread by means of an external tool to change the compression extent of the external spring so as to control the opening pressure of the annular conversion body; the working principle of the first stage pressure converting device is: (1) when the conversion body satisfies P_(mid)S_(left)+k_(inner)x≤P_(right)S_(right), the conversion body moves to the left, and then the annular flume is communicated with the side drain holes to supply water into the central transitional cavity to realize first stage pressure drop; (2) when the conversion body satisfies P_(mid)S_(left)+k_(inner)x≥P_(right)S_(right), the conversion body moves to the right, and then the annular flume is closed by the inner walls of the peripheral through holes to stop supplying water into the central transitional cavity; (3) if P_(right) is too large, in order to prevent extreme water pressure of P_(right) from damaging the inner wall of the drill hole in the water injection cavity through the pressure conversion assembly, the conversion body moves to the left under the action of the outside water source until the annular flume moves to the left end of the side drain hole and forms another closing role on the inner walls of the peripheral through holes, wherein P_(mid) is the water source pressure of the central transitional cavity, which is 0.8 to 1 MPa; P_(right) is the pressure of the supplied water source in the connected pipe, which is 1.5 MPa; S_(left) is the area of the left end surface of the conversion body; S_(right) is the area of the right end surface of the conversion body; k_(inner) is an elastic coefficient of the inner spring; and x is compression length; the working principle of the second stage pressure converting device is: (1) when the annular conversion body satisfies P_(left)S_(left)+k_(outer)x≤P_(mid)S_(right), the annular conversion body moves to the left, and then the limbers of No. 2 are communicated with the water collecting slots to inject low pressure water into the water injection cavity through the water diversion holes to realize second stage pressure drop; (2) when the annular conversion body satisfies P_(left)S_(left)+k_(outer)x≥P_(mid)S_(right), the annular conversion body moves to the right, and then the limbers of No. 2 are closed by the outer wall of the internal annular component to stop supplying water into the water injection cavity, wherein P_(left) is the observed water source pressure of the water injection cavity, which is 0.2 to 0.5 MPa; P_(mid) is the pressure of the water source in the central transitional cavity, which is 0.8 to 1 MPa; S_(left) is the contact area between water and the left end surface of the annular conversion body; S_(right) is the contact area between water and the right end surface of the annular conversion body; k_(outer) is an elastic coefficient of the external spring; and x is compression length; the control operation platform comprises a water release switch, a flow meter, a mechanical pressure gauge a total control switch and an electronic pressure gauge; the water release switch is responsible for releasing pressure water in the test probe after pressurized pressure testing completed so that the rubber bag is out of contact with the drill hole to facilitate the drilling rig in pushing the test probe; the total control switch is responsible for interruption of the external water source supply; the flow meter is responsible for displaying real-time water input from the external water source to the test probe; the mechanical pressure gauge is compared with the reading of the electronic pressure gauge for inspection; if the mechanical pressure gauge is roughly equal to the reading, then the pressure is effective.
 2. The graded pressure drop type multi stage water injection device based on fracture observation according to claim 1, wherein the plugging device at the front comprises a type I joint, a water leakage pipe, a type II joint and a rubber bag; the type I joint, the type II joint and the water leakage pipe are in threaded connection; the rubber bag is wrapped outside the water leakage pipe, is fixed outside the type I joint and the type II joint through a fastening iron ring, and forms a blocked cavity with the water leakage pipe; the external end of the type I joint is in threaded connection with a guide head; and the guide head has a guide effect and is used to guide the test probe to smoothly slide in the drill hole.
 3. The graded pressure drop type multi stage water injection device based on fracture observation according to claim 1, wherein the plugging device at the middle comprises a type II joint, a water leakage pipe, a type III joint and a rubber bag; the rubber bag is fixed outside the type II joint and the type III joint through a fastening iron ring, and a water leakage hole is formed in the water leakage pipe.
 4. The graded pressure drop type multi stage water injection device based on fracture observation according to claim 1, wherein the plugging device at the rear end comprises two type III joints, a water leakage pipe and a rubber bag; and the rubber bag is fixed between the two type III joints through a fastening iron ring.
 5. The graded pressure drop type multi stage water injection device based on fracture observation according to claim 3, wherein the plugging device at the rear end comprises two type III joints, a water leakage pipe and a rubber bag; and the rubber bag is fixed between the two type III joints through a fastening iron ring.
 6. The graded pressure drop type multi stage water injection device based on fracture observation according to claim 4, wherein the external part of the type III joints is in threaded connection with a circular baffle; the diameter of the circular baffle is larger than that of the rubber bag to prevent the rubber bag from falling; and the circular baffle and the type III joints are in threaded connection and are detachable to facilitate the replacement of the rubber bag.
 7. The graded pressure drop type multi stage water injection device based on fracture observation according to claim 5, wherein the external part of the type III joints is in threaded connection with a circular baffle; the diameter of the circular baffle is larger than that of the rubber bag to prevent the rubber bag from falling; and the circular baffle and the type III joints are in threaded connection and are detachable to facilitate the replacement of the rubber bag.
 8. The graded pressure drop type multi stage water injection device based on fracture observation according to claim 1, wherein the number of the water injection cavity is increased according to the need, and the design manner is identical.
 9. The graded pressure drop type multi stage water injection device based on fracture observation according to claim 4, wherein the number of the water injection cavity is increased according to the need, and the design manner is identical.
 10. A graded pressure drop type multi stage water injection method based on fracture observation, comprising the following steps: (1) constructing drill holes: constructing three to five drill holes with different directions and inclined angles in the region of rock mass to be detected through the drilling rig in accordance with predesigned construction requirements; the drill holes having a diameter of 89 mm and a length of about 70 m; and cleaning scraps in the drill holes; (2) installing equipment: installing all components of the test probe; successively connecting the drilling rig, the drill pipe, the high pressure resistant hose and the control operation platform; and then pushing the test probe to the initial positions of the drill holes through the drilling rig; (3) seal inspection: firstly, turning off a water release switch of the control operation platform; turning on the total control switch to provide detection water pressure for the test probe; conducting a plugging seal inspection on the rubber bag; conducting next operation if there is no obvious water leakage phenomenon; otherwise, returning to operation of step to inspect the connection and installation among all components until qualified; (4) detecting water leakage rate: conducting pressurized-water test after passing the seal inspection; starting the test probe to be in the initial position; turning off the water release switch on the control operation platform and turning on the total control switch to provide a high pressure water source for the test probe; allowing the water source to enter the blocked cavity through the connected pipe and the water leakage pipe; inflating the rubber bags of the plugging device at the front, the plugging device at the middle and the plugging device at the rear end to form a water injection cavity of No. 1 and a water injection cavity of No. 2 with the drill holes; adjusting the pressure of the external water source to gradually rise to 1.5 MPa for only allowing the pressure conversion assembly of the water injection cavity of No. 1 to inject low pressure water into the water injection cavity of No. 1, and recording the steady reading Q_(i1) of the flow meter after the reading of the flow meter is steady; continuously increasing the pressure of the external water source o 1.7 MPa for stopping supplying water into the water injection cavity of No. 1 at this moment because the first stage pressure converting device of the water injection cavity of No. 1 is turned off due to the increase of the pressure, and starting the pressure conversion assembly of the water injection cavity of No. 2 to inject water into the water injection cavity of No. 2; and recording the steady reading Q_(i2) of the flow meter after the reading of the flow meter is steady, and recording detection distances L_(i1) and L_(i2); (5) pressure relief propulsion: turning off the total control switch; turning on the water release switch to release the pressure of the blocked cavity; turning off the water release switch after the rubber bag is out of contact with the drill holes; taking another drill pipe to connect to the test probe; pushing the test probe to a next detection region through the drilling rig; and repeating the operation of step until all lengths of the drill holes is detected; (6) calculation and analysis: respectively drawing flow distribution maps in different drill holes according to the length of the drill holes and corresponding injected water leakage of drilling hole; analyzing fracture development and permeability characteristics at different positions within the length range of the drill holes; and further calculating failure range of the rock mass within different spatial ranges by combining with the inclined angles of the drill holes in different directions with accumulated successive water leakage length L_(n1)+L_(n2)(n=1+2+ . . . +k). 